When panoramic video images or full-circle video images are to be taken by a camera, a plurality of video images are taken while changing the direction of the camera, and the images are synthesized. Therefore, for example, the number of synthesized images is reduced by obtaining wide-angle images by using a fish-eye lens or the like. However, synthesis of a plurality of images cannot be avoided, and the plurality of images has to be synthesized without parallax. This is an essential problem derived from the fact that only the limited region in the front can be taken by the video images of the camera. As a system which takes a plurality of images and obtains synthesized images, a method using an electronic camera has been proposed. The electronic camera has: a lens barrel including an imaging optical system and an imaging element and a lens-barrel turning means which turns the lens barrel about an object-side principal point of the imaging optical system to the direction orthogonal to the optical axis of the imaging optical system; wherein, the lens barrel is turned by using the lens barrel turning means, divided object images are taken by taking images a plurality of times while sequentially changing the image-taking ranges, and the data of the plurality of images obtained by the imaging element for each image taking is recorded together with the information of the rotation angle of the lens barrel. Then, the obtained data of the plurality of images is synthesized into the data of one image based on the information of the rotation angle of the lens barrel. (For example, see Patent Document 1). In order to take video images by which the plurality of taken video images can be synthesized without misalignment, normally, rotation about a nodal point of the camera is carried out. The nodal point is the only point at which an object is optically reduced and rotated by a lens and converged before the object reaches a light-receiving surface of the camera. In order to rotate the camera about the nodal point, conventionally, a nodal-point adjustment device 210 as shown in FIG. 22 has been used. In FIG. 22, a front/back direction slide part 218 bored in a camera support member 214 for attaching a camera is provided so that the camera attached to a camera attachment part 216 can be moved to the front/back. The camera support member 214 is maintained at a fixed height by a supporting pillar 220. A base material 222 having a left/right direction slide part 224 bored therein is fixed to a certain fixed position by a screw 226. Furthermore, the screw 226 is inserted in a center position of a rotating mount (not shown) to fix the nodal-point adjustment device 210.
FIGS. 23A and 23B show a state in which the camera 10 is attached to the nodal-point adjustment device 210. A screw 212 is screw-tightened in an attachment screw hole of the camera, thereby fixing the camera 10. In order to adjust the position of the nodal point 14 of the camera 10 to the center of rotation of the mount, the front/back direction is adjusted by moving the position by the slide part 218 bored in the camera support member 214, and the left/right direction is adjusted by moving the position by the slide part 224 bored in the camera support base material 222. The adjustment is carried out, for example, by a so-called dry battery method in which two dry batteries are arranged and subjected to imaging so as to carry out adjustment to eliminate parallax. As a simple method to set the nodal point, a structure in which a screw hole is provided in the main body of the camera so that the nodal point is positioned at the center of rotation of the mount has been proposed (for example, see Patent Document 2).    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. H09-18750 Document    Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2006-178097 Document
In order to synthesize a plurality of images, parallax-free video images have to be taken; and, in order to do that, images are taken while the camera is directed in various directions centered on the nodal point of the camera. Generally, panoramic video images take a plurality of images in the horizontal direction. A nodal point adjustment device therefor sets the camera directed in the horizontal direction and then searches for the nodal point by taking images while moving the camera in the front/back left/right directions. When the nodal point is set, the camera is rotated in the horizontal direction at a fixed angle by a panoramic mount or the like to take video images.
In the case in which a nodal-point attachment screw hole which enables the nodal point to be easily set for the mount or the like is provided integrally with the camera, adjustment of the nodal point is not required. However, in these methods, when full-circle image taking is to be carried out, the nodal point adjustment device requires a nodal point adjusting operation again since the nodal point adjustment device is fixed with a changed direction of the camera, and there is a problem that a complicated operation has to be carried out many times. Moreover, the structure in which the nodal-point attachment screw hole is integrated with the camera can be applied only to the case in which the direction of the camera is fixed, and it has been impossible to take images with changed directions of the camera.